Please note that all benefits listed in TFA for 48V vs 12V are valid for 220V vs 110V, too.
Tesla shares 48V architecture with other automakers
381–390 of 504 posts
Re: Tesla shares 48V architecture with other automakers
#382Earlier quoted context omitted.
48V is good because a lot of safety standards have the cut off for 'extra-low voltage' at 60V DC, gives you a bit of margin (when battery charging it pushes up to be in the 50s for example). Some battery systems I've seen at 56 volts nominal too. so sometimes people do have a bit higher-voltage ELV systems. 48V still lets you touch both conductors with dry hands and it's still very unlikely for you to be able to get…
> requires extreme caution and safety procedures As long as the battery pack is still sealed and the interlock systems are undamaged and working correctly, it's no big deal. You follow the manufacturer's instructions to make it safe, then work on it like there's no voltage present. If the battery pack is broken or a prototype or whatever, yeah, then you need to think things through carefully before doing them. And ha…
GP was talking about the low voltage system (the 12-volt system in most cars) and choosing a voltage for it, not anything about the traction battery.
Re: Tesla shares 48V architecture with other automakers
#383Earlier quoted context omitted.
Yes but state of your body/skin (R) and current (I) is what matters with regard to 60 volts being really dangerous (also the current path as the article below states). 60 volts is nothing UNLESS you are completely wet or sweaty. "It is estimated at 150 ohms for completely wet skin (in water), 1000 ohms for sweaty skin, and 100,000 ohms to 500,000 ohms for dry skin." Assuming a worst-case scenario with dry skin provid…
> 60 volts is nothing UNLESS you are completely wet or sweaty. Ha, it’s always easy to tell when people have experience with these things. Doorbell wiring is 48V. Go hold those in each hand and tell me how impossible it is to feel if your hands are dry.
Doorbell voltage in the US is typically 12V or 24V AC in the US. I can’t feel that with dry hands.
You might be confused with POTS (landline phone service) which is 48V DC with all phones not in use.
Re: Tesla shares 48V architecture with other automakers
#384Earlier quoted context omitted.
My understanding was that nearly every production vehicle on the road is 12V and that Tesla and perhaps Audi as you mentioned are doing things differently. Who is using 400-800V systems? That sounds extremely dangerous.
Mercedes introduced their 48V hybrid in 2016. Kia in 2018. Peugeot just introduced theirs this year. Jalopnik was talking about the "48V revolution" in 2017: https://jalopnik.com/everything-you-need-to-know-about-the-u...
At least once delivered early then? Sharing tech 6 years before their annoncement of sharing it!
Alternative take: Everybody else was aware 48 V networks work as well for decades, there was just no real benefot in switching yet. And Tesla has nothing to do with it.
What's next, Tesla annoncing they will share the revolutionary tech of windscreens and doors?
Re: Tesla shares 48V architecture with other automakers
#385Earlier quoted context omitted.
> Or can and power over twisted pair. I was reading an anti-Musk subreddit over on Reddit and I think the cybertruck is doing this? They were mad that the cybertruck uses 48V and Ethernet cables, but to me, that seems perfect for CAN and power. We already use 48V (or similar) for PoE, and CAN needs a twisted pair... so why not buy that off the shelf instead of using a custom wiring harness? I don't think the cybertru…
Musk has publicly stated that CAN is too slow for modern cars, which is why they chose ethernet for the Cybertruck. https://youtube.com/watch?v=ky1Z2klPalw
CAN buses run into bandwidth issues at some point. Just remove all the OTA, car-as-a-service and de-facto surveillance crap, and one should be able to get away with CAN buses.
Nothing wrong with ethernet, but listening to Musks statements, especially in fields I have some not even deep knowledge, alwqys like listening to a very confident, but otherwise clueless, 1st semester student selling you semester 2 basics as the latest and hottest shit under the sun nobody else even considered possible so far...
Re: Tesla shares 48V architecture with other automakers
#386Earlier quoted context omitted.
Watts = Amps * Volts (or, more scientifically, P = I * V) If something draws 48 Watts of power, you can either supply it with 4 Amps @ 12 Volt, or 1 Amp @ 48 Volt. It's the amps that determine how thick the wiring needs to be, so by lowering the amperage, you lower the amount of wiring needed. I believe the only reason cars are 12 V is because that's a practical voltage to build lead-acid batteries at (which is actua…
This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you…
What matters is energy but what's being carried by the wire is charge. A given amount of charge can have more or less energy, which is what voltage is. So if you give each unit of charge more energy then you can carry more power by only moving the same amount of charge. You get a similar thing in mechanical systems: a shaft is sized based on the maximum amount of torque it can withstand, but the amount of power going through it also depends on the RPM. More RPM = more power, for the same amount of torque, so if you are for some reason limited in the size of the shaft, you can use a gearing mechanism to rotate it faster and then gear down the other side and get more power through a smaller shaft. It's just that in mechanical systems gears are a lot less convenient than changing voltages is in electrical systems.
(RPM and voltage are in fact related in EVs as well: generally speaking a higher voltage motor will be able to produce more power for the same amount of space and materials, but mostly by spinning faster, not producting more torque. You then need to gear it down to be practical in a car. But the trend is that things that make higher voltages and higher RPMs possible (the technology in transistors, insulation, bearings) are already cheap or getting cheaper, while things that make higher currents and torques possible (generally more raw material like copper and steel) are staying the same or getting more expensive. So EVs in general are pushing to higher voltages for lots of things)
Re: Tesla shares 48V architecture with other automakers
#387Could I have 48V for my GPU power supply as well, please?
Re: Tesla shares 48V architecture with other automakers
#388Earlier quoted context omitted.
This makes such little sense to me. I'm probably just stupid, but if the same amount of power is flowing through the wire, don't you need the same size of wire? A higher voltage system will push more energy through the same component, so you need thicker wires. If you up the resistance of the component to consume the same amount of energy as before, you arrive at the same size of wire you were using before, don't you…
A higher voltage system enables the same energy at a lower amperage, so constrained to wanting to do a particular thing (loud stereo, bright headlights, ...), higher voltages result in lower amperages. I'll opt to not try to explain that intuitively, hoping that somebody else chimes in. For the other half, "why do amps determine wire size?" Amps are coulombs per second -- how much electrical stuff moves through a cro…
Edit: Heat released is also proportional to the temperature differential between the wire and the outside world, as well as a constant associated with how well it's thermally insulated. The wire temperature rises till either some sort of breakdown occurs or that rate of heat release balances the rate of heat production. The spirit of that original comment is correct, but this feels like a nuance that might matter to somebody new to the topic.
Re: Tesla shares 48V architecture with other automakers
#389Earlier quoted context omitted.
I think another big part of it is that DC switches tend to get expensive above 12V. Cheap AC switches work fine at higher voltage, because the arc is self-extinguishing as it passes through zero twice per cycle, but DC doesn't do that so you can end up with an arc that doesn't extinguish itself, which, aside from not turning the thing off when you want to, burns out the electrical contacts.
Now we have MOSFETS and IGBTs that can switch DC without sparks. I suspect most DC switching in the Cybertruck is relayed through these. (Except the main contactor and pyro fuse of course.)
And given that this is a Tesla, it wouldn't really have had many mechanical switches in the first place. Maybe the turn indicator? Which could happily run at 5 volts or something and blink the lights via CAN bus messages.
Re: Tesla shares 48V architecture with other automakers
#390Does anyone know where a civilian (me) could access a pdf?